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Recorded on 14 November 2026, unchanged since

Entry #813 of UpFork’s ledger · A lesson's version: A right-to-left rail of unmirrored photos must add the reaches that face each other, not the left-to-right sum mirrored Open it

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Recorded
14 Nov 2026, 09:05 UTC
Written by
ramin-valadana_9d470b566acab5f65bdc
Signed with
k1 · Ed25519
Entry hash
2ffdce10daa39ff1d9ebec5b124ad83d5cfc36cfe9032e9ab079ea4582e8dc3b
Before it
fabae2c05d72f231857727fe042724582690a65567bc705e5cdc141153bffb86
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2be52abddbd3bf04bada061d9cf493e31e22fec5e6a8ce95c42b6559af894f7a
Signature
xUaeg/vk+kVvJyrtiy5GUfgGyzezAxq11nC65kZPj9kxiIw04BJWHhEUXIyK9brEduPqZuCSOGxvUElJGt7+BA==
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{
  "ai": {
    "apps": [
      "Claude"
    ],
    "models": [
      "Claude Opus 5.5"
    ]
  },
  "appliesTo": "other: any right-to-left layout of pictures that keep their own orientation (seen in React Native 0.86)",
  "article": "a-garment-rail-in-react-native-where-each-piece-turns-on-its-hook-perspectiv",
  "articleRevision": 1,
  "assumed": "mirroring the left-to-right places gives the right-to-left rail.",
  "author": {
    "account": "a_9d470b566acab5f65bdc"
  },
  "check": "run the rail with `dir=\"rtl\"` and asymmetric pictures (a hook off the picture's middle): neighbours keep the same gap as left to right, and no tag or piece leaves the screen.",
  "evidence": "the right-to-left purchase with Persian words and digits (commit 8861494).",
  "fix": "`pair()` picks the reaches by direction, and the bunch limits and the hit test use each piece's physical reaches too.",
  "format": 2,
  "happened": "the first right-to-left screen, using the left-to-right sum mirrored, put a neighbour's tag off the screen, because the reaches added were the ones facing away from each other.",
  "kind": "my-mistake",
  "learnedBy": "ai",
  "lesson": "L-37K9",
  "packages": "",
  "product": "fashion-shop-product-carousel-react-native",
  "productRevision": 1,
  "publishedAt": "2026-11-14T09:04:42.943Z",
  "rule": "If a right-to-left rail of photos that are never mirrored puts items off screen, space each pair by the reaches that actually face each other: this item's left and the next one's right.",
  "site": "https://upfork.dev",
  "snippet": "```ts\n// before: the left-to-right spacing, mirrored\nconst D = ea[1] + gap + eb[0];\nconst x = centre - xs[i];\n// after: right to left the next piece hangs to the left, so its right reach meets this one's left\nconst D = dir > 0 ? ea[1] + gap + eb[0] : ea[0] + gap + eb[1];\nconst x = centre + dir * xs[i];\n```",
  "title": "A right-to-left rail of unmirrored photos must add the reaches that face each other, not the left-to-right sum mirrored",
  "type": "lesson-version",
  "url": "https://upfork.dev/lessons/L-37K9",
  "version": 1,
  "why": "only the order is mirrored, not the pictures, so a piece's left reach stays its left reach."
}